The primary objective of this study is to characterize in vitro the regulation of apoptotis by a viral Bcl-2 homolog encoded by the M11 gene of murine gammaherpesvirus 68 (MHV-68). The M11 open reading frame is located within a cluster of viral genes that may be latency-associated in MHV-68. This gene cluster is present in related rhadinoviruses including KSHV and herpesvirus saimiri (HSV), but the presence of a Bcl-2 homolog within this cluster is unique to MHV-68. However, KSHV, HVS, and other gammaherpesvirus genomes including that of EBV also encode Bcl-2 homologous proteins with which M11 is potentially comparable. In the proposed in vitro studies both recombinant virus constructs and M11 expressing cell lines will be used to explore M11 function. Precisely designed MHV-68 recombinants along with conventional expression studies using wild type virus are also expected to provide initial insight into the expression of M11 in specific cell types in vitro providing preliminary data that may be pursued if warranted in future in vivo studies beyond the scope of the current proposal. Specific goals of the proposed study include: 1) Analysis of expression of M11 and adjacent genes during lytic infection of NIH/3T3 cells and during experimental infection of selected murine B-lymphocyte and macrophage cell lines; 2) Assessment of putative M11 anti-apoptotic activity in selected cell lines expressing M11; 3) Determination of whether M11 associates with itself and/or other Bcl-2 family proteins and whether recognized dimerization domains may be involved in any such associations that are detected; 4) Construction of MHV-68 recombinants with the M11 gene deleted (and expression of neighboring genes intact) to determine whether M11 is essential for lytic replication in vitro and whether M11 significantly regulates apoptotic mechanisms during experimental infection of selected cell lines.